Integrated method for producing middle distillate with a recycling loop in hydrotreatment

ABSTRACT

Method of treating petroleum feedstocks comprising the hydrotreatment of said feedstocks followed by hydrocracking of at least one part of the hydrotreatment effluent. Cooling and separating the hydrocracking effluent into a hydrogen-rich gas efflux and a liquid efflux. Fractionating the liquid effluent into converted hydrocarbon products having boiling points lower than 340° C. and an unconverted liquid fraction having a boiling point higher than 340° C. Hydrotreating a diesel-fuel-type liquid hydrocarbon feedstock and separating the effluent into a hydrogen-rich gas efflux and a liquid efflux. Fractionating the liquid efflux into at least one light gas fraction, a naphtha fraction, and a middle distillate fraction having a boiling point higher than 150° C. and compressing the gas efflux in a hydrogen makeup compressor supplying the hydrotreatment and hydrocracking steps comprising at least 2 stages, with said gas efflux being injected and compressed in an intermediate stage of said compressor before being recycled upstream.

FIELD OF THE INVENTION

This invention relates to a method for treatment of petroleum feedstockswhose objective is to maximize the quantity and the quality of middledistillate fractions that are produced.

The method for hydrocracking vacuum distillates or DSV is a key refiningmethod that makes it possible to produce, from excess heavy feedstocksthat cannot be readily upgraded, the lighter fractions such asgasolines, jet fuels, and light diesel fuels that the refiner strives toproduce in order to adapt his production to demand. Certainhydrocracking methods make it possible also to obtain a highly purifiedresidue that can constitute excellent bases for oils or an easilyupgradable feedstock in a catalytic cracking unit, for example. One ofthe effluents that is particularly targeted by the hydrocracking methodis the middle distillate (fraction that contains the diesel fuelfraction and the kerosene fraction). This catalytic method does not makeit possible to transform the DSV in its entirety into light fractions.After fractionation, a more or less large proportion of an unconvertedDSV fraction, referred to as UCO or UnConverted Oil according to Englishterminology, therefore remains. The conversion level and the selectivityof the method can be adjusted with the option of UCO recycling at theinlet of the hydrotreatment reactor or at the inlet of the hydrocrackingreactor (so-called 1.5-step mode). The addition of a conversion reactoror hydrocracking reactor to the UCO recycling is another means to adjustthe conversion and the selectivity (so-called 2-step mode).

The method for hydrodesulfurization of diesel fuels makes it possible toreduce the amount of sulfur contained in a diesel fuel fraction whileminimizing the conversion of the feedstock into lighter products (gas,naphtha). The hydrodesulfurization feedstock can consist of straight-rundiesel fuel according to English terminology or diesel fuel obtainedfrom atmospheric fractionation of crude oil, the Light Vacuum Gasoil Oilaccording to English terminology or light vacuum distillate, the LCO ordistillate obtained from a conversion method (FCC, coking . . . ), of adiesel fuel feedstock obtained from biomass conversion (esterification,for example), by themselves or in a mixture, for example.

The partial hydrogen pressure required for this method is lower than thepartial hydrogen pressure in the hydrocracking device. It is commonpractice for these two methods to be present in the same refinerywithout being integrated. However, they are based on very similar methodschemes, constituted by a feedstock furnace, fixed-bed reactors,hydrogen-recycling compressors, and more or less complex high-pressureseparation sections.

This invention consists in integrating these two methods so as to reduceinvestment costs and energy expenditure of the middle distillateproduction complex. Inter-unit integration is based on a pooling ofequipment.

Prior Art

The patent U.S. Pat. No. 7,507,325 B2 describes the integration betweena unit for soft hydrocracking or Mild Hydrocracking (MHC) according toEnglish terminology and a unit for hydrotreatment of diesel fuels, bothin fixed beds. The integration is based on the recycling of the dieselfuel fraction obtained from MHC to the HDT unit so as to obtain a dieselfuel that complies with the Euro V specification. The hydrogen makeup ofthe complex is supplied by a common compressor and is advantageouslysent in its entirety to the hydrotreatment unit so as to maximize thepartial hydrogen pressure. The hydrogen makeup of the mild hydrocrackingunit is produced from the separation section of the hydrotreatment unit.This operating mode requires that the units operate at compatiblepressure levels. In this method, the entire hydrogen supply is sent intothe hydrotreatment step, and the diesel fuel produced in thehydrocracking step is recycled in the step for hydrodesulfurization ofthe diesel fuels.

The patent U.S. Pat. No. 5,447,621 describes an integrated method fortreatment of the middle distillate fraction, in which the diesel fuelfraction obtained from the 1-step fractionation of a hydrocrackingdevice is recycled to a hydrotreatment step for the purpose of improvingits properties. The preheating of this diesel fuel fraction is carriedout by the heat recovered at the effluent from the hydrocracking step.The separation of the HDT effluent is carried out through the stripperside of the fractionation column of the hydrocracking device. Thecompression system of the makeup hydrogen is common to the two units andin the first place supplies the HDT step, and then the gaseous effluentfrom the hydrogen-rich hydrotreatment supplies the HCK step viaadditional compression stages.

The research work of the applicant led to discovering that a pooling ofthe makeup hydrogen compression system and an inter-unit thermalintegration can be carried out and makes it possible to maximize thepartial hydrogen pressure in the unit for hydrodesulfurization of dieselfuel with total iso-pressure, and primarily to limit the operating costslinked to utilities and to reduce the initial investment cost, whilemaintaining the quality of the products.

SUMMARY OF THE INVENTION

In particular, this invention relates to a complex for hydrotreatmentand hydrocracking of petroleum fractions whose purpose is to maximize,in quality and quantity, the production of the middle distillatefraction.

The hydrocracking method treats hydrocarbon feedstocks containing atleast 20% by volume and preferably at least 80% by volume of compoundsboiling above 340° C., with said method comprising at least thefollowing steps:

-   a) The hydrotreatment of said feedstocks in the presence of hydrogen    and at least one hydrotreatment catalyst, at a temperature of    between 200 and 450° C., under a pressure of between 2 and 18 MPa,    at a volumetric flow rate of between 0.1 and 6 h-1, and with an    amount of hydrogen introduced such that the volumetric ratio of    liter of hydrogen/liter of hydrocarbon is between 100 and 2,000 L/L,-   b) The hydrocracking of at least one part of the effluent obtained    from step a), with the hydrocracking step b) being carried out, in    the presence of hydrogen and at least one hydrocracking catalyst, at    a temperature of between 250 and 480° C., under a pressure of    between 2 and 25 MPa, at a volumetric flow rate of between 0.1 and 6    h⁻¹, and with an amount of hydrogen introduced such that the    volumetric ratio of liter of hydrogen/liter of hydrocarbon is    between 100 and 2,000 L/L,-   c) Passing into at least one heat exchanger of at least said    effluent obtained from step b) in which said effluent is cooled by    exchanging the liquid hydrocarbon feedstock entering into step f) in    at least one exchanger,-   d) The gas/liquid separation of the cooled effluent obtained from    step c) to produce at least one hydrogen-rich gas efflux and at    least one liquid efflux,-   e) The fractionation of said liquid effluent obtained from step d)    into at least one fraction comprising the converted hydrocarbon    products having boiling points lower than 340° C. and an unconverted    liquid fraction having a boiling point higher than 340° C.,-   f) The hydrotreatment of a liquid hydrocarbon feedstock comprising    at least 95% by weight of compounds boiling at a boiling point of    between 150 and 400° C., preheated in advance in step c), with said    step f) being carried out in the presence of hydrogen and at least    one hydrotreatment catalyst, at a temperature of between 200 and    390° C., under a pressure of between 2 and 16 MPa, at a volumetric    flow rate of between 0.2 and 5 h-1, and with an amount of hydrogen    introduced such that the volumetric ratio of liter of hydrogen/liter    of hydrocarbon is between 100 and 2,000 L/L,-   g) The gas/liquid separation of the effluent obtained from step f)    for producing at least one hydrogen-rich gas efflux and at least one    liquid efflux,-   h) The fractionation of the liquid effluent obtained from step g)    making possible the separation of at least one light gas fraction, a    naphtha fraction, and a middle distillate fraction having a boiling    point higher than 150° C.,-   i) The compression of the hydrogen-rich gas effluent obtained from    step g) in a hydrogen makeup compressor supplying steps a), b)    and f) and comprising n stages, with n being an integer that is    greater than or equal to 2, with said hydrogen-rich gas effluent    being injected and compressed in an intermediate stage of said    compressor before being recycled upstream from step f).

One advantage of this invention is to provide a method integrating ahydrocracking method in one or two steps with a method forhydrodesulfurization of diesel fuels making it possible to maximize thepartial hydrogen pressure in the diesel fuel hydrotreatment unit attotal iso-pressure and to limit the weighted mean temperature of thecatalyst in the step for hydrotreatment of diesel fuels thanks to theimplementation of a compression step i) in a single compressor forhydrogen makeup in several stages, supplying steps a), b) and f) of themethod according to the invention.

Another advantage of this invention is to provide a method that byintegration of two methods makes it possible to reduce operating costslinked to utilities and to reduce the initial investment cost.

DETAILED DESCRIPTION OF THE INVENTION Feedstocks

This invention relates to a method for hydrocracking hydrocarbonfeedstocks called source feedstocks, containing at least 20% by volumeand preferably at least 80% by volume of compounds boiling above 340°C., preferably above 350° C., and in a preferred manner between 340 and580° C. (i.e., corresponding to compounds containing at least 15 to 20carbon atoms).

Said hydrocarbon feedstocks can advantageously be selected from amongVGO (Vacuum Gas Oil) according to English terminology or vacuumdistillates (DSV), such as, for example, the diesel fuels obtained fromdirect distillation of crude or conversion units, such as FCC, such asLCO or Light Cycle Oil according to English terminology, the coker orthe visbreaking as well as feedstocks obtained from units for extractionof aromatic compounds from lubricating oil bases or obtained fromdewaxing with solvent of lubricating oil bases, or else distillatescoming from desulfurization or hydroconversion of RAT (atmosphericresidues) and/or RSV (vacuum residues), or else the feedstock canadvantageously be a deasphalted oil, or feedstocks obtained from biomassor else any mixture of the above-cited feedstocks and preferably VGO.

The paraffins obtained from the Fischer-Tropsch method are excluded.

In general, said feedstocks have a boiling point T5 higher than 340° C.,and better yet higher than 370° C., i.e., 95% of the compounds presentin the feedstock have a boiling point higher than 340° C., and betteryet higher than 370° C.

The nitrogen content of the source feedstocks treated in the methodaccording to the invention is usually higher than 500 ppm by weight,preferably between 500 and 10,000 ppm by weight, in a more preferredmanner between 700 and 4,000 ppm by weight, and in an even morepreferred manner between 1,000 and 4,000 ppm by weight. The sulfurcontent of the source feedstocks treated in the method according to theinvention is usually between 0.01 and 5% by weight, in a preferredmanner between 0.2 and 4% by weight, and in an even more preferredmanner between 0.5 and 3% by weight.

The feedstock can optionally contain metals. The cumulative content ofnickel and vanadium of the feedstocks that are treated in the methodaccording to the invention is preferably less than 1 ppm by weight.

The asphaltene content is generally less than 3,000 ppm by weight, in apreferred manner less than 1,000 ppm by weight, in an even morepreferred manner less than 200 ppm by weight.

The feedstock can optionally contain asphaltenes. The asphaltene contentis generally less than 3,000 ppm by weight, in a preferred manner lessthan 1,000 ppm by weight, and in an even more preferred manner less than200 ppm by weight.

In the case where the feedstock contains resin-type and/orasphaltene-type compounds, it is advantageous first to switch thefeedstock to a catalyst bed or adsorbent bed that is different from thehydrocracking or hydrotreatment catalyst.

Step a)

In accordance with the invention, the method comprises a step a) forhydrotreatment of said feedstocks in the presence of hydrogen and atleast one hydrotreatment catalyst, at a temperature of between 200 and450° C., under a pressure of between 2 and 18 MPa, at a volumetric flowrate of between 0.1 and 6 h⁻¹, and with an amount of hydrogen introducedsuch that the volumetric ratio of liter of hydrogen/liter of hydrocarbonis between 100 and 2,000 L/L.

The operating conditions such as temperature, pressure, hydrogenrecycling rate, hourly volumetric flow rate, can be very variable basedon the nature of the feedstock, the quality of the desired products, andinstallations used by the refiner.

Preferably, the hydrotreatment step a) according to the invention iscarried out at a temperature of between 250 and 450° C., in a verypreferred manner between 300 and 430° C., under a pressure of between 5and 16 MPa, at a volumetric flow rate of between 0.2 and 5 h⁻¹, and withan amount of hydrogen introduced such that the volumetric ratio of literof hydrogen/liter of hydrocarbon is between 300 and 1,500 L/L.

Conventional hydrotreatment catalysts can advantageously be used,preferably that contain at least one amorphous substrate and at leastone hydro-dehydrogenating element selected from among at least oneelement of non-noble groups VIB and VIII, and most often at least oneelement of group VIB and at least one element of the non-noble groupVIII.

Preferably, the amorphous substrate is alumina or silica-alumina.

Preferred catalysts are selected from among the catalysts NiMo, NiW orCoMo on alumina and NiMo or NiW on silica-alumina.

An organic compound can be used during the preparation of the catalystor else can be present in the porosity of the final catalyst.

The effluent obtained from the hydrotreatment step and entering into thehydrocracking step a) generally comprises a nitrogen content that ispreferably less than 300 ppm by weight and preferably less than 50 ppmby weight.

In the hydrotreatment step, said feedstocks are advantageouslydesulfurized and denitrified before the latter is sent to thehydrocracking catalyst of step b) itself, in particular in the casewhere the latter comprises a zeolite.

This intensive hydrotreatment of the feedstock entrains only a limitedconversion of the feedstock, into lighter fractions, which remainsinsufficient and is therefore to be completed in the more activehydrocracking catalyst.

Step b)

In accordance with the invention, the method comprises a step b) forhydrocracking at least one part of the effluent obtained from step a),and preferably in its entirety, with said step b) being carried out, inthe presence of hydrogen and at least one hydrocracking catalyst, at atemperature of between 250 and 480° C., under a pressure of between 2and 25 MPa, at a volumetric flow rate of between 0.1 and 6 h⁻¹, and withan amount of hydrogen introduced such that the volumetric ratio of literof hydrogen/liter of hydrocarbon is between 100 and 2,000 L/L.

Preferably, the hydrocracking step a) according to the invention iscarried out at a temperature of between 320 and 450° C., in a verypreferred manner between 330 and 435° C., under a pressure of between 3and 20 MPa, at a volumetric flow rate of between 0.2 and 4 h⁻¹, and withan amount of hydrogen that is introduced such that the volumetric ratioof liter of hydrogen/liter of hydrocarbon is between 200 and 2,000 L/L.

These operating conditions used in the method according to the inventiongenerally make it possible to achieve conversions per pass of productshaving boiling points lower than 340° C., and, better, lower than 370°C., greater than 15% by weight, and in an even more preferred mannerbetween 20 and 95% by weight.

The hydrocracking method according to the invention covers the fields ofpressure and conversion ranging from mild hydrocracking to high-pressurehydrocracking. Mild hydrocracking is defined as hydrocracking leading tomoderate conversions, generally less than 40%, and operating at lowpressure, preferably between 2 MPa and 6 MPa. The high-pressurehydrocracking is generally carried out at higher pressures of between 5MPa and 20 MPa, in such a way as to obtain conversions higher than 50%.

The hydrocracking method according to the invention can advantageouslybe carried out in one or two step(s), independently of the pressure atwhich said method is implemented. It is carried out in the presence ofone or more hydrocracking catalyst(s), in one or more reaction unit(s)equipped with one or more reactor(s) in a fixed bed or in a boiling bed,optionally separated by one or more high-pressure and/or low-pressureseparation sections.

According to a first embodiment according to the invention, thehydrocracking method according to the invention is implemented accordingto a so-called one-step mode. In this case, no separation step isimplemented between the hydrotreatment step a) and the hydrocrackingstep b). The entire effluent exiting from the hydrotreatment step a) isinjected into said hydrocracking step b) itself, and it is only thenthat separation of the products formed takes place in the fractionationstep c) according to the invention.

According to a second embodiment of said one-step method, a step forincomplete separation of ammonia from the effluent obtained from thehydrotreatment step a) of said source hydrocarbon feedstocks isimplemented. Preferably, said separation is advantageously carried outby means of an intermediate hot flash. The hydrocracking step b)according to the invention is then carried out in the presence ofammonia in an amount that is smaller than the amount that is present insaid source hydrocarbon feedstocks, preferably less than 1,500 ppm byweight, in a more preferred manner less than 1,000 ppm by weight, and inan even more preferred manner less than 800 ppm by weight of nitrogen.

According to another embodiment according to the invention, thehydrocracking method according to the invention is implemented accordingto a so-called two-step mode. The second hydrocracking step will bedescribed below.

The hydrotreatment step a) and the hydrocracking step b) canadvantageously be carried out in the same reactor or in differentreactors. In the case where they are produced in the same reactor, thereactor comprises multiple catalytic beds, with the first catalytic bedscomprising the hydrotreatment catalyst(s) and the next catalytic bedscomprising the hydrocracking catalyst(s).

Hydrocracking Catalyst of Step b)

The hydrocracking catalyst(s) used in the hydrocracking step b) areconventional hydrocracking catalysts of the bifunctional type combiningan acid group with a hydrogenating group and optionally at least onebonding matrix.

Preferably, the hydrocracking catalyst(s) comprise(s) at least one metalof group VIII selected from among iron, cobalt, nickel, ruthenium,rhodium, palladium and platinum, and preferably cobalt and nickel and/orat least one metal of group VIB selected from among chromium,molybdenum, and tungsten, by itself or in a mixture, and preferably fromamong molybdenum and tungsten.

Hydrogenating groups of the NiMo, NiMoW, NiW type are preferred.

Preferably, the metal content of group VIII in the hydrocrackingcatalyst(s) is advantageously between 0.5 and 15% by weight andpreferably between 2 and 10% by weight, with the percentages beingexpressed in terms of percentage by weight of oxides.

Preferably, the metal content of group VIB in the hydrocrackingcatalyst(s) is advantageously between 5 and 25% by weight and preferablybetween 15 and 22% by weight, with the percentages being expressed interms of percentage by weight of oxides.

The catalyst(s) can also optionally comprise at least one promoterelement deposited on the catalyst and selected from the group formed byphosphorus, boron, and silicon, optionally at least one element of groupVIIA (fluorine, chlorine preferred), and optionally at least one elementof group VIIB (manganese preferred), optionally at least one element ofgroup VB (niobium preferred).

Preferably, the hydrocracking catalyst(s) comprise(s) a zeolite selectedfrom among the USY zeolites, by itself or in combination, with otherzeolites from among the following zeolites: beta, ZSM-12, IZM-2, ZSM-22,ZSM-23, SAPO-11, ZSM-48, ZBM-30, by themselves or in a mixture. In apreferred manner, the zeolite is the USY zeolite by itself.

The hydrocracking catalyst(s) can optionally comprise at least oneporous or poorly-crystallized mineral matrix of the oxide type selectedfrom among aluminas, silicas, silica-aluminas, aluminates, alumina-boronoxide, magnesia, silica-magnesia, zirconia, titanium oxide, clay, bythemselves or in a mixture, and preferably alumina.

A preferred catalyst comprises and preferably consists of at least onemetal of group VI and/or at least one metal of non-noble group VIII, a Yzeolite, and an alumina binder.

An even more preferred catalyst comprises and preferably consists ofnickel, molybdenum, phosphorus, a Y zeolite, and alumina.

Another preferred catalyst comprises and preferably consists of nickel,tungsten, a Y zeolite and an alumina, or silica-alumina.

In a general way, the catalyst(s) used in the hydrocracking step b)advantageously contain(s):

-   0.1 to 60% by weight of zeolite-   0.1 to 40% by weight of at least one element of groups VIB and VIII    (% oxide)-   0.1 to 99.8% by weight of matrix (% oxide)-   0 to 20% by weight of at least one element selected from the group    formed by P, B, Si (% oxide), preferably 0.1-20%-   0 to 20% by weight of at least one element of group VIIA, preferably    0.1 to 20%-   0 to 20% by weight of at least one element of group VIIB, preferably    0.1 to 20%-   0 to 60% by weight of at least one element of group VB, preferably    0.1 to 60%.

With the percentages being expressed in terms of percentage by weight inrelation to the total catalyst mass, the sum of percentages of elementsconstituting said catalyst being equal to 100% of the total catalystmass.

The hydrocracking catalyst(s) used according to the invention is (are)preferably subjected to a sulfurization treatment making it possible totransform, at least in part, the metal radicals into sulfide before theyare brought into contact with the feedstock to be treated. Thisactivation treatment by sulfurization is well known to one skilled inthe art and can be carried out by any method already described in theliterature.

Regardless of the embodiment of the hydrocracking method, the methodaccording to the invention comprises a fractionation step c) comprisinga fractionation unit placed downstream from the reactors, which makes itpossible to separate the various products obtained from thehydrocracking reactor(s) of step b).

Step c)

In accordance with the invention, the method comprises a step c) forpassing into at least one heat exchanger of at least said effluentobtained from step b), in which said effluent is cooled by exchangingthe liquid hydrocarbon feedstock entering into step f) in at least oneexchanger.

Said step c) is advantageously implemented in a number of heatexchangers of between 1 and 10, and preferably between 1 and 4, and in avery preferred manner 3.

In a preferred embodiment, at least one part of the effluent obtainedfrom the hydrotreatment step a) in the case where steps a) and b) areimplemented in different reactors, and/or at least one part andpreferably the entirety of the effluent obtained from the secondhydrocracking step j) in the case where the latter is implemented, canalso be cooled by passing into at least one exchanger of said step c) byexchanging the liquid hydrocarbon feedstock entering into step f),preferably mixed with a stream of makeup and recycling hydrogen obtainedfrom step i) and supplying step f), in at least one exchanger. In thiscase, the exchanges between the various streams may take place in thesame exchanger or in different exchangers.

Step c) therefore makes possible the inter-unit thermal integration bymaking possible the preheating of at least the diesel-fuel-type liquidhydrocarbon feedstock of said hydrotreatment step f), by exchange withat least the effluent obtained from the hydrocracking step b) and/orobtained from the hydrotreatment step a), and/or obtained from thesecond hydrocracking step e).

According to this invention, the use of a furnace dedicated to thepreheating of the diesel-fuel-type liquid hydrocarbon feedstock of saidhydrotreatment step f) in normal operation is therefore no longernecessary. The result is a reduction in the investment and operatingcosts linked to the utilities (consumption of fuel gas) of the method.

Step d)

In accordance with the invention, the method comprises a step d) forgas/liquid separation of the cooled effluent obtained from step c) forproducing at least one hydrogen-rich gas efflux and at least one liquidefflux. Preferably, step d) is carried out at high pressure.

After cooling in step c), the effluent obtained from the hydrocrackingstep b) is sent into a gas/liquid separation step d) at high pressure.Said separation step d) is advantageously carried out by means of a hotseparator followed by a cold separator or by means of a single coldseparator. A series of hot and cold separators at high and mediumpressure can also be present.

The hot separator operates at high temperature, high pressure, with atemperature of between 50 and 450° C., preferably between 100 and 400°C., even more preferably between 200 and 300° C., and a pressurecorresponding to the output pressure of b) minus the pressure drops. Thecold separator operates at low temperature, high pressure, with atemperature of between 0 and 400° C., preferably between 0 and 400° C.,even more preferably between 0 and 100° C., and a pressure correspondingto the output pressure of b) minus the pressure drops.

The hydrogen-rich gas efflux can advantageously be recycled in at leastthe hydrotreatment step a) and/or the hydrocracking step b) and/or inthe second hydrocracking step j). Said gas effluent can advantageouslybe mixed with the makeup hydrogen obtained from step i) before itsrecycling in said step(s).

Step e)

In accordance with the invention, the method comprises a step e) forfractionation of said liquid effluent obtained from step d) into atleast one fraction comprising the converted hydrocarbon products havingboiling points lower than 380° C., preferably lower than 370° C., and ina preferred manner lower than 340° C., and an unconverted liquidfraction that has a boiling point higher than 340° C., preferably higherthan 370° C., and in a preferred manner higher than 380° C., also calledUCO or “unconverted oil” according to English terminology.

Preferably, said fractionation step d) comprises a first separation stepcomprising a separation means such as, for example, a separator tank ora steam stripper preferably operating at a pressure of between 0.5 and 2MPa, which has as its object to carry out a separation of hydrogensulfide (H₂S) from at least one hydrocarbon effluent produced duringsteps a), b) and in an optional manner e). The hydrocarbon effluent,obtained from this first separation, can advantageously undergoatmospheric distillation, and in some cases the combination ofatmospheric distillation and vacuum distillation. The distillation hasas its object to carry out a separation between the convertedhydrocarbon products, i.e., generally having boiling points lower than380° C., preferably lower than 370° C., and in a preferred manner lowerthan 340° C., and an unconverted liquid fraction (UCO) (residue).

According to another variant, the fractionation step consists only of anatmospheric distillation column.

According to another variant, the separator (e) preferably consists ofat least one distillation column, and in a very preferred manner a steamstripper followed by atmospheric distillation.

The converted hydrocarbon products having boiling points lower than 380°C., preferably lower than 370° C., and in a preferred manner lower than340° C., are advantageously distilled at atmospheric pressure to obtainmultiple converted fractions with a boiling point of at most 380° C.,preferably at most 370° C., and in a preferred manner at most 340° C.,and preferably a C1-C4 light gas fraction, at least one gasolinefraction, and at least one kerosene and diesel fuel middle-distillatefraction.

The unconverted liquid fraction having a boiling point higher than 340°C. (UCO) can advantageously be recycled entirely or partially, in thehydrotreatment step a) and/or in the hydrocracking step b) and/or in thesecond hydrocracking step e) in such a way as to adjust the rate ofconversion or selectivity of the method according to the invention.

Optional Step j)

In another embodiment of the method according to the invention, saidmethod is implemented according to a so-called two-step hydrocrackingmethod. In this case, at least one part and preferably all of the liquidfraction having a boiling point higher than 340° C. (UCO), which isunconverted during the first hydrocracking step b) and obtained from thefractionation step e), is sent into a second hydrocracking step j).

Preferably, said second hydrocracking step j) is implemented underconditions that are identical to or different from those of saidhydrocracking step b) and in the presence of a hydrocracking catalystthat is identical to or different from the one implemented in said stepb).

Preferably, said second hydrocracking step j) is implemented, in thepresence of hydrogen and at least one hydrocracking catalyst, at atemperature of between 250 and 480° C., preferably between 320 and 450°C., and in a very preferred manner between 330 and 435° C., under apressure of between 2 and 25 MPa, preferably between 3 and 20 MPa, at avolumetric flow rate of between 0.1 and 6 h-1, and preferably between0.2 and 3 h-1, and with an amount of hydrogen introduced such that thevolumetric ratio of liter of hydrogen/liter of hydrocarbon is between100 and 2,000 L/L, and preferably between 200 and 2,000 L/L.

The description of the catalyst used in said second hydrocracking stepj) is identical to the one of the catalyst used in said first step b).

Preferably, the catalyst used in step j) is different from the one ofstep b). The effluent produced in the second hydrocracking step j) canadvantageously, in its entirety or partially, be sent into thegas/liquid separation step d) and/or into step c) of the methodaccording to the invention.

Step f)

In accordance with the invention, the method comprises a step f) forhydrotreatment of a liquid hydrocarbon feedstock comprising at least 95%by weight of compounds boiling at a boiling point of between 150 and400° C., preferably between 150 and 380° C., and in a preferred mannerbetween 200 and 380° C., preferably preheated in step c), with said stepf) being carried out in the presence of hydrogen and at least onehydrotreatment catalyst, at a temperature of between 200 and 390° C.,under a pressure of between 2 and 16 MPa, at a volumetric flow rate ofbetween 0.2 and 5 h-1, and with an amount of hydrogen introduced suchthat the volumetric ratio of liter of hydrogen/liter of hydrocarbon isbetween 100 and 2,000 L/L.

Preferably, said liquid hydrocarbon feedstock treated in step f) isadvantageously selected from among the liquid hydrocarbon feedstocksobtained from the direct distillation of a crude oil (or straight runaccording to English terminology) and preferably selected from among thestraight-run diesel fuel, the Light Vacuum Gasoil Oil (LVGO) accordingto English terminology, or the light vacuum distillate, and the liquidhydrocarbon feedstocks obtained from a coking unit (coking according toEnglish terminology), preferably coker diesel fuel, from a visbreakingunit (visbreaking according to English terminology), a steam-crackingunit (steam cracking according to English terminology) and/or from acatalytic cracking unit (Fluid Catalytic Cracking according to Englishterminology), preferably the LCO (light cycle oil) or light diesel fuelsobtained from a catalytic cracking unit, and a diesel fuel feedstockobtained from biomass conversion (esterification, for example); saidfeedstocks can be taken by themselves or in a mixture.

According to the invention, the diesel-fuel-type liquid hydrocarbonfeedstock treated in step f) is advantageously preheated, preferably ina mixture with a stream of makeup and recycling hydrogen obtained fromstep i), by passing into step c) according to the invention. Saidfeedstock is advantageously preheated at the temperature that makes itpossible to reach the WABT or weighted mean temperature in the catalystbeds of the hydrotreatment reactor of step f).

According to a preferred embodiment, said feedstock is preheated bypassing into at least one exchanger of step c) by heat exchange with atleast the effluent obtained from the hydrocracking step b) and/orobtained from the hydrotreatment step a) in the case where steps a) andb) are implemented in different reactors, and/or obtained from thesecond hydrocracking step j) in the case where the latter isimplemented.

In a very preferred embodiment, a first heat exchange is carried out forall or part of the effluent obtained from the hydrotreatment step a), asecond exchange can be carried out for at least one part and preferablyall of the effluent obtained from the hydrocracking step b), and a lastexchange can be carried out for all or part of the effluent obtainedfrom the second hydrocracking step j).

Preferably, the hydrotreatment step f) according to the invention iscarried out at a temperature of between 230 and 350° C., in a verypreferred manner between 250 and 350° C., under a pressure of between 5and 16 MPa, at a volumetric flow rate of between 0.2 and 4 h⁻¹, and withan amount of hydrogen introduced such that the volumetric ratio of literof hydrogen/liter of hydrocarbon is between 300 and 1,500 L/L.

The description of the hydrotreatment catalysts used in step f) isidentical to those used in step a). They can be identical to ordifferent from those used in step a).

Step g)

In accordance with the invention, the method comprises a step g) forgas/liquid separation of the effluent obtained from step f) forproducing at least one hydrogen-rich gas efflux and at least one liquidefflux.

Preferably, step g) is carried out at high pressure.

Said separation step g) is advantageously carried out by means of a hotseparator followed by a cold separator or by means of a single coldseparator. A series of hot and cold separators at high and mediumpressure can also be present.

The hot separator operates at high temperature, high pressure, with atemperature of between 50 and 450° C., preferably between 100 and 400°C., even more preferably between 200 and 300° C., and a pressurecorresponding to the output pressure of f) minus the pressure drops. Thecold separator operates at low temperature, high pressure, with atemperature of between 0 and 400° C., preferably between 0 and 400° C.,even more preferably between 0 and 100° C., and a pressure correspondingto the output pressure of f) minus the pressure drops.

According to the invention, the hydrogen-rich gas efflux obtained fromstep g) is sent into a compression step i).

According to the invention, the liquid effluent obtained from step g) issent into a fractionation step h).

Step h)

In accordance with the invention, the method comprises a step h) forfractionation of the liquid effluent obtained from step g) making itpossible to separate at least one light gas fraction, a naphthafraction, and a middle distillate fraction having a boiling point higherthan 150° C.

Preferably, said fractionation step h) comprises a separation stepcomprising a separation means, such as, for example, a separator tank ora steam stripper operating preferably at a pressure of between 0.5 and 2MPa, which has as its object to carry out a separation of hydrogensulfide (H₂S) from at least one hydrocarbon effluent produced in thehydrotreatment step f). Preferably, said step h) produces a stream oflight gases (C1-C4), a naphtha stream with a boiling point lower than150° C., and a middle distillate stream with a boiling point higher than150° C. and preferably boiling between 150 and 370° C.

Step i)

In accordance with the invention, the method comprises a step i) forcompression of the hydrogen-rich gas effluent obtained from step g) in ahydrogen makeup compressor supplying steps a), b) and f), and optionallyj), and comprising n stages, with n being an integer that is greaterthan or equal to 2, said hydrogen-rich gas effluent being injected andcompressed in an intermediate stage of said compressor before beingrecycled upstream from the hydrotreatment step f), preferably upstreamfrom step c).

Preferably, the compressor comprises a number of stages n of between 2and 5, preferably between 2 and 4, and in a particularly preferred wayequal to 3.

The steps for hydrotreatment of diesel fuel f) and the steps forhydrocracking vacuum distillate implemented in steps a), b) andoptionally j) of this invention are conducted at distinct pressures. Theimplementation of said compression step i) in a single hydrogen makeupcompressor in several stages, supplying steps a), b) and optionally j)and step f), makes it possible to use different pressures for each ofsaid steps a), b) and optionally j) and step f).

Thus, the hydrotreatment step a) and the hydrocracking step b) andoptionally j) are advantageously supplied by hydrogen coming from theoutlet of the last compression stage of said step i), and thehydrotreatment step f) is advantageously supplied by the outlet from anintermediate compression stage of said step i), i.e., at a lowerpressure.

In the particular embodiment where n is equal to 3, the hydrogenobtained from the outlet of the second compression stage supplies thehydrotreatment step of f) and is mixed with the diesel-fuel-type liquidhydrocarbon feedstock entering into said step f).

According to a particular embodiment, the partial hydrogen pressure inthe hydrotreatment reactor of step f), PH₂, is between 3.0 and 8.0 MPa.

These optimized partial hydrogen pressure values are made possible bythe mode of operation of the compression step i) of this invention. Thegas effluent comprising the recycling hydrogen produced in thehydrotreatment step f) and separated in step g) is not picked up here bya dedicated compressor but by the common compression system implementedin step i).

According to the invention, said hydrogen-rich gas effluent obtainedfrom step g) is injected and compressed in an intermediate stage of saidcompressor before being recycled upstream from the hydrotreatment stepf). In the preferred mode where n is equal to 3, said gas effluent isinjected between the first and second compression stages and compressedin the second compression step.

Said hydrogen-rich gas effluent obtained from step g) is advantageouslymixed with the makeup hydrogen of the method according to the inventionat the intake of an intermediate compression stage, and preferablybetween the first and second compression steps in the case where n isequal to 3, which has the effect of diluting it and increasing itshydrogen purity.

Said hydrogen-rich gas effluent obtained from step g) is then compressedby this intermediate stage and preferably the second stage, before beingrecycled upstream from the hydrotreatment step f).

The hydrogen stream supplying the hydrotreatment step f) from the outletof the intermediate stage, and preferably from the second step in thecase where n is equal to 3, therefore consists of a mixture of makeuphydrogen and recycling gas coming from the hydrotreatment step f) andseparated in step g).

This mode of operation makes it possible to dilute the recycling gaswith the makeup hydrogen of the method with high purity, therefore anincrease of the partial hydrogen pressure of the hydrotreatment step f).It primarily makes possible a reduction in the overall investment thanksto the elimination of the dedicated recycling compressor.

DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the invention and its preferred embodiments.

The vacuum distillate feedstock (1), optionally in a mixture with theunconverted fraction (34) obtained from the fractionation step e), issent into a first hydrotreatment step a) with a hydrogen makeup stream(2), completed by the recycled hydrogen (3) obtained from a gas/liquidseparation step d). The effluent of the first hydrotreatment step a)supplies the first hydrocracking step b) via the line (4) or via theline (5) that once cooled by passing into an exchanger of step c) issent back to the hydrocracking step b) via the line (6). Optionally, apart of the unconverted fraction is recycled in step b) via the pipe(35). The monitoring of the weighted mean temperature (WABT) of thehydrocracking reactor can thus be carried out in two ways: either by aquenching of recycled hydrogen-rich gas effluent (31) mixed with theline (4), or by an energy recovery step c) that makes it possible topreheat the diesel-fuel-type feedstock of the hydrotreatment step f).

The effluent (7) of the first hydrocracking step b) is first cooled instep c) by passing into an exchanger, which makes possible the transferof calories to the diesel fuel feedstock entering into thehydrotreatment step (f) via the pipe (18) in a mixture with therecycling and makeup hydrogen via the pipe (19). The cooled effluent (8)exiting from the exchanger is sent to a separation step d). The lattermakes it possible to obtain at least one hydrogen-rich gas efflux (3)and a liquid efflux (9) that contains for the most part convertedfractions and a smaller proportion of unconverted fractions. The liquidstream (9) is then sent into a fractionation step e) that makes itpossible to obtain a middle-distillate-type fraction (12) and a heavierfraction than the diesel fuel (13), an acid gas stream containing H₂S(10), and a naphtha-type fraction (11).

The unconverted fraction obtained from the fractionation step e) canoptionally constitute the vacuum distillate feedstock (14) sent to thesecond hydrocracking step (j). The feedstock (14) is optionally mixedwith a recycled hydrogen-rich gas effluent (32) and obtained from theseparation step (d) and with a makeup hydrogen effluent (33). Aftercooling by passing into an exchanger of step c) via the line (16), theeffluent of the second hydrocracking step j) can optionally be sent tothe separation step (d) at high pressure via the line (15). The caloriesavailable at the outlet of step (j) can therefore be used in step (c)for passing by an exchanger making possible thermal integration betweenunits so as to preheat the feedstock of the hydrotreatment step (f). Thecooled effluent (17) is directed toward the separation step (d) in amixture with the effluent of the first hydrocracking step (8).

The diesel fuel feedstock (18) is sent with a stream of recycling andmakeup hydrogen (19) into a preheating step at high temperature bypassing into an exchanger (c) making it possible to reach the WABTrequired in the hydrotreatment step (f). This step (c) takes placewithin heat exchangers operating with, on the one hand, the feedstock(18) of the HDT and, on the other hand, the effluents (7) and/or (5)produced in steps (a) and (b), and in an optional manner the effluent(16) of step (e). The preheated feedstock (20) is treated in thehydrotreatment reactor of step (f). Its effluent (21) is, after cooling,sent to the separation step (g) at high pressure. The latter makes itpossible to obtain at least one hydrogen-rich gas effluent (22) and atleast one liquid effluent (23). The liquid effluent (23) is then sent toa fractionation step h) making it possible to obtain at least one middledistillate fraction (26) and a stream of acid gas containing H₂S (24). Anaphtha fraction (25) can also be separated. The fractionation step (h)is carried out in a preferred manner within a steam stripping column.

The single compression system of step (i), and common to twohydrocracking and hydrotreatment units, is supplied by the gas stream(27) containing all of the makeup hydrogen necessary to the method.According to a preferred variant shown in the figure, the compression iscarried out via 3 stages. The hydrogen stream (29) recovered at theoutlet from the 1^(st) compression stage is mixed with the recycling gas(22) of the diesel fuel HDT unit produced in step (g). The mixture (28)is sent to the intake of the 2^(nd) compression stage. The pressurelevel obtained at the outlet from the 2^(nd) stage is compatible withthe pressure level required in the hydrotreatment step (f). The gasstream (19) thus supplies the diesel fuel hydrotreatment unit with thenecessary makeup and recycling hydrogen. The hydrogen contained in thestream (30) is compressed in a3^(rd) stage. At the outlet, the pressurelevel obtained makes it possible to supply steps a) and b) with themakeup hydrogen that is necessary (2) to the hydrotreatment andhydrocracking reactions of vacuum distillates. A stream of makeuphydrogen (33) is sent to the 2^(nd) hydrocracking step j).

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forthuncorrected in degrees Celsius and, all parts and percentages are byweight, unless otherwise indicated.

The entire disclosures of all applications, patents and publications,cited herein and of corresponding application No. FR 1759088, filed Sep.29, 2017 are incorporated by reference herein.

The examples illustrate the invention without limiting its scope.

EXAMPLES Example 1 Not in Accordance With the Invention

The complex for production of middle distillates consists of two units:one unit for hydrotreatment of diesel fuel and one unit forhydrocracking of vacuum distillates in two steps.

According to Example 1, the two units follow a standard scheme and areoperated independently from one another. Only the hydrogen makeupcompressor is common to the two units.

Feedstocks

The hydrotreatment unit treats a diesel fuel feedstock described inTable 1:

TABLE 1 Properties of the Diesel Fuel Feedstock Properties Unit DieselFuel Mixture Flow Rate t/h 319.9 d15 4 t/m3 0.8628 PI TBP ° C. 143 PFTBP ° C. 383 S % by weight 0.82 N wtppm 632

The hydrotreatment unit treats a vacuum distillate feedstock (DSV)described in Table 2:

TABLE 2 Properties of the DSV Feedstock Properties Unit DSV Mixture FlowRate t/h 478.7 d15 4 t/m3 0.955 PI TBP ° C. 350 PF TBP ° C. 760 S % byweight 2.08 N wtppm 2,142

Hydrotreatment of Diesel Fuels

The diesel fuel feedstock described in Table 1 is injected into apreheating step comprising a furnace dedicated to the hydrotreatmentunit and then sent to the hydrotreatment reactor under the followingconditions:

TABLE 3 Operating Conditions of the Reactor - Diesel Fuel HDT Unit UnitOperating Conditions WABT SOR ° C. 340 Catalyst — HR 1248 H2/HC Nm3/Sm3800 Partial H2 Pressure MPa 78.0 VVH h−1 0.95

The catalyst used is a NiMo alumina catalyst marketed by the AxensCompany. The effluent is sent into a separation step consisting of aheat recovery train and then separation at high pressure including arecycling compressor dedicated to the diesel fuel HDT unit. This sectionmakes it possible to separate, on the one hand, hydrogen, hydrogensulfide and ammonia, and, on the other hand, the effluent supplying astripper. The stripping step makes it possible to fractionate theeffluent into a gas stream containing H₂S and light ends, a naphthastream, and a stream of middle distillates at the desired specification.

Two-Step DSV Hydrocracking Device

The DSV feedstock is injected into a preheating step and then into ahydrotreatment reactor under the following conditions:

TABLE 4 Operating Conditions of the Reactor 1 - DSV HCK Unit UnitOperating Conditions WABT SOR ° C. 384 Catalyst — HRK 1448 H2/HC Nm³/Sm³1,200 Partial H2 Pressure MPa >14.5 VVH h⁻¹ 0.60

The catalyst used is a NiMo alumina catalyst marketed by the AxensCompany.

The effluent from this reactor is then mixed with a hydrogen stream tobe cooled and then injected into a second so-called hydrocrackingreactor R2 operating under the conditions of Table 5:

TABLE 5 Operating Conditions of Reactor 2 - DSV HCK Unit Unit OperatingConditions WABT SOR ° C. 393 Catalyst — HYK 743 H₂/HC Nm³/Sm³ 1,200Partial H₂ Pressure MPa >14.5 VVH h⁻¹ 2.70

The catalyst used is a metal zeolite catalyst marketed by the AxensCompany. R1 and R2 constitute the first step of the hydrocrackingdevice; the effluent of R2 is then sent into a separation step thatconsists of a train of heat recovery and then separation at highpressure including a recycling compressor and making it possible toseparate, on the one hand, hydrogen, hydrogen sulfide, and ammonia, and,on the other hand, the effluent that supplies a stripper and then anatmospheric fractionation column so as to separate the streamsconcentrated in H2S, naphtha, kerosene, diesel fuel at the desiredspecification, and an unconverted heavy stream. This unconverted heavystream is injected into a preheating step and then into a hydrocrackingreactor R3 constituting the second hydrocracking step. This reactor R3is implemented under conditions set forth in Table 6:

TABLE 6 Operating Conditions of Reactor 3 - DSV HCK Unit Unit OperatingConditions WABT SOR ° C. 370 Catalyst — HDK 766 H2/HC Nm³/Sm³ 1,000Partial H2 Pressure MPa >12.5 VVH h⁻¹ 1.50

The catalyst used is a metal catalyst on amorphous silica-aluminamarketed by the Axens Company.

The effluent of R3 is then injected into a separation step at highpressure, and the hydrogen-rich gas stream is recycled.

The middle distillate fraction produced in the hydrocracking device andrecovered in the fractionation column complies with the Euro Vspecifications; in particular, it has less than 10 ppm by weight ofsulfur.

Investment Costs Hydrotreatment of Diesel Fuel

An estimation of the cost of the diesel fuel HDT unit (reference year2015 and Europe zone) and the distribution of this investment by type ofequipment is provided in Table 7.

TABLE 7 Estimation of the Investment - Diesel Fuel HDT Unit Number SetupCosts Type of Equipment of Items (thousands of USD) Furnaces 1 4,054Reactors 1 12,143 Columns 2 3,067 Tanks 8 3,782 Heat Exchangers 18 9,977Cooling Towers 3 5,033 Pumps and Driving Machines 10 8,416 Compressorsand Driving Machines 1 8,497 Storage Units 0 0 Miscellaneous 5 1,534Method's Margin of Error 0 5,650 Total Unit Cost 49 62,153

Two-Step DSV Hydrocracking Device

An estimation of the cost of the DSV HCK unit (reference year 2015 andEurope zone) and the distribution of this investment by type ofequipment is provided in Table 8.

TABLE 8 Estimation of the Investment - DSV HCK Unit Number Setup CostsType of Equipment of Items (thousands of USD) Furnaces 3 14,531 Reactors5 65,518 Columns 13 20,735 Tanks 27 24,915 Heat Exchangers 47 37,442Cooling Towers 23 22,454 Pumps and Driving Machines 56 31,637Compressors and Driving Machines 13 66,849 Storage Units 0 0Miscellaneous 2 1,108 Method's Margin of Error 0 28,519 Total Unit Cost189 313,707

Example 2 In Accordance With the Invention

In the example in accordance with the invention, the integration ofunits is more advanced. A common compression system is installed: therecycling gas of the diesel fuel HDT unit is compressed by the 2^(nd)stage of the hydrogen makeup compressor. The feedstock preheatingfurnace dedicated to the diesel fuel HDT unit is replaced by exchangercalendars recovering the energy available to the inter-reactor of theDSV HCK unit.

Feedstocks

The method according to Example 2 is carried out with the samefeedstocks as in Example 1.

Primary Operating Conditions Hydrotreatment of Diesel Fuel

The method according to Example 2 is carried out according to the sameoperating conditions as in Example 1.

The pooling of the compression system makes possible, however, animprovement in the partial hydrogen pressure of the diesel fuel HDTunit: the latter, by a dilution effect of the recycling gas with the H₂makeup of the complex, observes a rise of +2 points (8 MPa), which isbeneficial for the service life of the catalyst.

Two-Step DSV Hydrocracking Device

The method according to Example 2 is carried out according to the sameoperating conditions as in Example 1.

Investment Costs Hydrotreatment of Diesel Fuel

An estimation of the cost of the diesel fuel HDT unit (reference year2015 and Europe zone) according to the invention and the distribution ofthis investment by type of equipment is provided in Table 9.

TABLE 9 Estimation of the Investment According to the Invention - DieselFuel HDT Unit Number Setup Costs Type of Equipment of Items (thousandsof USD) Furnaces 0 0 Reactors 1 12,143 Columns 2 3,067 Tanks 8 3,782Heat Exchangers 20 12,384 Cooling Towers 3 5,033 Pumps and DrivingMachines 10 8,416 Compressors and Driving Machines 0 0 Storage Units 0 0Miscellaneous 5 1,534 Method's Margin of Error 0 4,636 Total Unit Cost49 50,995

The invention makes it possible to eliminate the furnace and therecycling compressor, which constitute significant cost items in adiesel fuel HDT unit. The increase in investment cost amounts to $11.2million, or a relative reduction of 18%.

The visible increase in the exchangers item (+$2.4 million) reflects thereplacement of the furnace by a heat exchanger for the HCK effluent. Theadditional cost is less than the price of the furnace in question.

Two-Step DSV Hydrocracking Device

An estimation of the cost of the DSV HCK unit (reference year 2015 andEurope zone) according to the invention and the distribution of thisinvestment by type of equipment is provided in Table 10.

TABLE 10 Estimation of the Investment According to the Invention - DSVHCK Unit Number Setup Costs Type of Equipment of Items (thousands ofUSD) Furnaces 3 14,531 Reactors 5 65,518 Columns 13 20,735 Tanks 2724,915 Heat Exchangers 46 37,050 Cooling Towers 23 22,454 Pumps andDriving Machines 56 31,637 Compressors and Driving Machines 13 72,361Storage Units 0 0 Miscellaneous 2 1,108 Method's Margin of Error 029,031 Total Unit Cost 188 319,339

The reduction in investment cost noted on the HDT side of diesel fuelsis reflected on the HCK side as increases in the compressor items andthe HCK investment (+$5.6 M). The relative increase is very small sinceit is less than 2%.

The 2^(nd) stage is resized to be able to recycle the hydrogen-rich gasof the diesel fuel HDT unit. The additional cost (+$5.5 M) remains wellbelow that of the cost of the recycling compressor.

Overall, the invention therefore makes possible an improvement in theinvestment in the complex.

To this improvement in investment cost, we should add increases inoperating costs linked to utilities. The consumption in fuel gas of thefurnace dedicated to diesel fuel HDT is canceled according to theinvention. The same holds true for the consumption of high-pressuresteam, making possible the driving of the recycling compressor dedicatedto said unit. An estimation of the annual reductions on these two itemsfor a Europe zone and a reference year 2015 is proposed in Table 11.

TABLE 11 Reduction in Outlays Linked to Utilities, According to theInvention Hourly Reduction in Utility Price Consumption Annual OutlaysFuel Gas 33.73 Gcal/h  9.9 Gcal/h $2.80 M/year High-Pressure Steam$41.30/ton 21.2 ton/h $7.38 M/year

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A hydrocracking method for treating hydrocarbon feedstocks containingat least 20% by volume and preferably at least 80% by volume ofcompounds boiling above 340° C., said method comprising: a)hydrotreatment of said feedstocks in the presence of hydrogen and atleast one hydrotreatment catalyst, at a temperature of between 200 and450° C., under a pressure of between 2 and 18 MPa, at a volumetric flowrate of between 0.1 and 6 h⁻¹, and with an amount of hydrogen introducedsuch that the volumetric ratio of liter of hydrogen/liter of hydrocarbonis between 100 and 2,000 L/L, b) hydrocracking of at least one part ofthe effluent obtained from step a), with the hydrocracking step b) beingcarried out, in the presence of hydrogen and at least one hydrocrackingcatalyst, at a temperature of between 250 and 480° C., under a pressureof between 2 and 25 MPa, at a volumetric flow rate of between 0.1 and 6h⁻¹, and with an amount of hydrogen introduced such that the volumetricratio of liter of hydrogen/liter of hydrocarbon is between 100 and 2,000L/L, c) passing into at least one heat exchanger of at least saideffluent obtained from step b) in which said effluent is cooled byexchanging the liquid hydrocarbon feedstock entering into step f) in atleast one exchanger, d) gas/liquid separation of the cooled effluentobtained from step c) to produce at least one hydrogen-rich gas effluxand at least one liquid efflux, e) fractionation of said liquid effluentobtained from step d) into at least one fraction comprising theconverted hydrocarbon products having boiling points lower than 340° C.and an unconverted liquid fraction having a boiling point higher than340° C., f) hydrotreatment of a liquid hydrocarbon feedstock comprisingat least 95% by weight of compounds boiling at a boiling point ofbetween 150 and 400° C., preheated in advance in step c), with said stepf) being carried out in the presence of hydrogen and at least onehydrotreatment catalyst, at a temperature of between 200 and 390° C.,under a pressure of between 2 and 16 MPa, at a volumetric flow rate ofbetween 0.2 and 5 h⁻¹, and with an amount of hydrogen introduced suchthat the volumetric ratio of liter of hydrogen/liter of hydrocarbon isbetween 100 and 2,000 L/L, g) gas/liquid separation of the effluentobtained from step f) for producing at least one hydrogen-rich gasefflux and at least one liquid efflux, h) fractionation of the liquideffluent obtained from step g) making possible the separation of atleast one light gas fraction, a naphtha fraction, and a middledistillate fraction having a boiling point higher than 150° C., i)compression of the hydrogen-rich gas effluent obtained from step g) in ahydrogen makeup compressor supplying steps a), b) and f) and comprisingn stages, with n being an integer that is greater than or equal to 2,with said hydrogen-rich gas effluent being injected and compressed in anintermediate stage of said compressor before being recycled upstreamfrom step f), j) hydrocracking of at least one part of the liquidfraction having a boiling point higher than 340° C. that is unconvertedduring the first hydrocracking step b) and obtained from thefractionation step e), with said second hydrocracking step j) beingcarried out in the presence of hydrogen and at least one hydrocrackingcatalyst, at a temperature of between 250 and 480° C., under a pressureof between 2 and 25 MPa, at a volumetric flow rate of between 0.1 and 6h-1, and with an amount of hydrogen introduced such that the volumetricratio of liter of hydrogen/liter of hydrocarbon is between 100 and 2,000L/L.
 2. Method according to claim 1, in which the hydrocarbon feedstockstreated in said method and sent into step a) are selected from among thehydrocarbon feedstocks containing at least 80% by volume of compoundsboiling between 340-580° C.
 3. Method according to claim 1, in which thehydrocarbon feedstocks treated in said method and sent into step a) areselected from among the vacuum distillates (DSV) selected from among thediesel fuels obtained from direct distillation of crude or conversionunits and the distillates coming from the desulfurization orhydroconversion of atmospheric residues and/or vacuum residues,deasphalted oils, and the feedstocks obtained from biomass or else anymixture of the feedstocks cited above.
 4. Method according to claim 1,in which the hydrocracking catalyst(s) used in step b) comprise(s) atleast one metal of group VIII selected from among iron, cobalt, nickel,ruthenium, rhodium, palladium and platinum, and/or at least one metal ofgroup VIB selected from among chromium, molybdenum, and tungsten, byitself or in a mixture, and a zeolite selected from among the USYzeolites, by itself or in combination, with other zeolites from amongthe following zeolites: beta, ZSM-12, IZM-2, ZSM-22, ZSM-23, SAPO-11,ZSM-48, ZBM-30, by themselves or in a mixture.
 5. Method according toclaim 1, in which at least one part of the effluent obtained from thehydrotreatment step a) and/or at least one part of the effluent obtainedfrom the second hydrocracking step j) is/are cooled by passing into atleast one exchanger of said step c) by exchanging the liquid hydrocarbonfeedstock entering into step f), mixed with a stream of makeup andrecycling hydrogen obtained from step i) and supplying step f), in thesame exchanger or in different exchangers.
 6. Method according to claim1, in which said step c) is implemented in a number of heat exchangersof between 1 and
 10. 7. Method according to claim 1, in which saidliquid hydrocarbon feedstock treated in the hydrotreatment step f) isselected from among the diesel fuel obtained from atmosphericfractionation of crude oil, the Light Vacuum Gasoil Oil (LVGO) accordingto English terminology or light vacuum distillate, and the liquidhydrocarbon feedstocks obtained from a coking unit (coking according toEnglish terminology), preferably coker diesel fuel, from a visbreakingunit (visbreaking according to English terminology), a steam-crackingunit (steam cracking according to English terminology) and/or from acatalytic cracking unit (Fluid Catalytic Cracking according to Englishterminology), preferably the LCO (light cycle oil) or light diesel fuelsobtained from a catalytic cracking unit, and a diesel fuel feedstockobtained from biomass conversion.
 8. Method according to claim 1, inwhich the hydrotreatment step f) according to the invention is carriedout at a temperature of between 230 and 350° C., in a very preferredmanner between 250 and 350° C., under a pressure of between 5 and 16MPa, at a volumetric flow rate of between 0.2 and 4 h⁻¹, and with anamount of hydrogen introduced such that the volumetric ratio of liter ofhydrogen/liter of hydrocarbon is between 300 and 1,500 L/L.
 9. Methodaccording to claim 1, in which the compressor of step i) comprises anumber of stages n of between 2 and
 4. 10. Method according to claim 9,in which said compressor comprises 3 stages.
 11. Method according toclaim 1, in which the hydrotreatment step a) and the hydrocracking stepb) are supplied by hydrogen coming from the outlet of the lastcompression stage of said step i), and the hydrotreatment step f) issupplied by the outlet of an intermediate compression stage of said stepi).
 12. Method according to claim 10, where n is equal to 3, wherein thehydrogen coming from the outlet of the second compression stage whichsupplies the hydrotreatment step f is mixed with the liquid hydrocarbonfeedstock entering into said step f).
 13. Method according to claim 10,in which said hydrogen-rich gas effluent obtained from step g) isinjected between the first and second compression stages and compressedin the second compression stage.
 14. Method according to claim 10, inwhich said hydrogen-rich gas effluent obtained from step g) is mixedwith the makeup hydrogen at the intake between the first and secondcompression stages and then compressed by the second stage, before beingrecycled upstream from the hydrotreatment step f).